Defect structure and mechanical behavior of BLiIn

Abstract

The defect structure of LiIn β phase has been studied by means of X-ray lattice parameter and bulk density measurements. The lattice parameter vs. composition curve shows a maximum at the stoichiometric composition and decrease on both sides of the stoichiometry. The compositional dependence of the density data does not fit the theoretical density calculated for several single-defect models from the lattice parameter data. Rather, the defect structure of LiIn is characterized by two types of defect: vacancies in the lithium sublattice and lithium antistructure atoms in the indium sublattice. The mechanical properties of the polycrystalline LiIn have been investigated by microhardness and compression tests as a function of temperature and composition. The ductile-to-brittle transition temperature, the hardness and the yield strength increase with increasing lithium content and these results are correlated with the defect structure. The compositional dependence of the mechanical properties is due mainly to the effect of the antistructure defects. The temperature and composition dependence of the strain rate sensitivity as well as the magnitude of the activation volume and its stress dependence suggest that a Peierls mechanism is the rate-controlling plastic deformation process in LiIn specimens deformed at low temperatures. Grain boundary sliding, which was observed in LiIn specimens deformed at high temperatures, becomes more important in the plastic deformation at temperatures above about 300°C.